Article of manufacture and method of producing the same



' 1938- F. H. \DRIGGS ETAL 2,125,895

ARTICLE OF MANUFACTURE AND METHOD OF PRODUCING THE SAME I Filed July 10,1954 2 Sheets-Sheet 1 ATTORNEY Aug. 9, 1938. F. H. DRIGGS ET AL ARTICLE,OF MANUFACTURE AND METHOD OF PRODUCING THE SAM 2 Sheets-Sheet 2 FiledJuly 10, 1934 INVENTOR F H.D/?/6 6 6 ATTORNEY Patented Aug. 9, 1938UNITED STATES narrow: or more AND METHOD CTUBE F PRODUCING THE SAMEFrank H. Briggs, Highland Park, IlL, and Barry W. Highritcr, Verona, N.1., assignors, by mesne assignments,

to Westinghouse Electric and Manufacturing Company, East Pittsburgh,Pa., a corporation oi Pennsylvania Application July 10, 1934, Serial No.734,450

15 Claims. (Cl. 250-35) This invention relates to an improved article ofmanufacture and to a novel method for producing the same. In its morespecific aspect the invention is directed to an improvement in anodesfor x-ray tubes and .to the method for producing the same. x-ray tubegenerally consists of an envelope containing an anode and a thermioniccathode therein. The cathode is incandesced for supplyin: electrons andwhen an appropriate potential is applied between these electrodes, theelectrons emanating from the cathode are forced to the anode and bombardthe target portion of the same to produce X-rays. During this bombardingaction some of the energy possessed by the electrons is converted toheat energy at the anode.

; The anode may consist of a target .composed of a refractory metal,generally tungsten, embedded in a backing of metal, such as copper,having high thermal and high electrical conductivity characteristics. Inthe course of X-ray tube operation, it is found that X-ray tubessometimes fail because of anode fusion. In some cases serious crackingof the copper close to the target occurs. The cracking generally takesplace along the grain boundaries approximately one grain diameterdistant from the edge of the target. The cracking first takes place onthe surface of the copper around the target and gradually increases inboth amount and scope until it extends underneath the target as well.Thus there is formed an isolated zone of copper around the tungstenwhich is in poor thermal contact with the remainder of the copperbacking. When this condition is reached the high temperature, which thiscopper in contact with the tungsten attains during operation, issufficient to melt the copper thus causing a failure in the tube.

Probably the basic cause of this type of failure in the copper lies inthe wide difierence in thermal coefllclents of expansion of tungsten andcopper. At room temperature the coefiicient of expansion of copper isabout five times that of tungsten. During operation of the tube theentire anode is probably subjected to temperature changes varying fromroom temperature to about 500 C. It is our belief that the expansion andcontraction of the tungsten and copper due to these temperaturevariations cause the cracking in the copper to take place.

, It is in order to obviate this difficulty that this invention isprimarily concerned. Briefly this disadvantage is removed by providing areinforcement in the copper in the vicinity of the target to take upsome of the stresses which would otherwise be taken up by the copper perso. That is, the reinforcing means which we provide in the copperadjacent the target reduces the stresses so that the stresses that areborne by the copper to are less than those necessary to cause coppercracking. In addition, the reinforcing means so distributes the stressesas to prevent the stresses from exceeding the tensile strength of theboundary between adjacent crystals.

An object of our invention is to provide an improved clad metal.

Another object of our invention is to provide an improved anode for anelectric discharge device such as an X-ray tube.

A still further object of our invention is to provide a novel method forproducing the same.

These and other objects of our invention will be readily understood fromthe following description and drawings wherein,

Figure 1 represents a fragmentary view partly in section of an X-rayanode embodying our invention, with the section taken. along line I--Iof Figure 2;

Figure 2 represents a plan view of an X-ray anode embodying ourinvention, with the embedded reinforcing elements shown by dotted lines;

Figure 3 represents a form employed and illustrates one of the steps offorming the reinforcing element; v

Figure 4 is a perspective view only partially completed and showing theconfiguration of the reinforcing element;

Figure 5 represents the apparatus employed for carrying out one of thesteps of our invention;

Figure 6 represents the product obtained after can'ying out one step ofour invention in the apparatus illustrated in Figure 5;

Figure 7 represents the apparatus employed in carry g out another stepof our invention;

Figure 8 illustrates a modification of Figure 1 and embodying ourinvention; and

Figure 9 illustrates a further modification of Figure l and embodyingour invention.

As illustrated in Figures 1 and 2, an improved anode embodying ourinvention comprises a copper rod III of high thermal and electricconductivity characteristics. has an angular face at about twentydegrees to the longitudinal axis of said rod. Embedded in said rod andforming a portion of said angular face is a target ll composed oftungsten or the like.

The width of the target II is about half that of said angular face andits length is about threequarters that of said face. The target is sodisposed with relation to said rod that its eifective face is flush withthe copper portion of said rod which, together define the angular face.The upper extremity of the target is flush with the upper extremity ofsaid rod and the target is located midway between the sides of saidface.

For the prevention of'copper cracking in the copper adjacent thelongitudinal and transverse edges of the target we provide a reinforcingmeans The target end of the rod it. The reinforcing means it maycomprise a plurality of strands of refractory material of high tensilestrength. The material may be composed of tungsten, molybdenum or thelike whose meltin point is higher than that of copper. Reinforcing meansthat we have found suitable for our purposes consists of a basket weaveconstruction partially illustrated in Figure 4 and composed on tungstenwires that may be of- 5, 10, or 17 mil.

diameter. Although all three sizes of wires were equally good asreinforcing means, we found that the 10 mil. size was the most desirablefrom the standpoint of ease of handling and general sta-'turnsofthewireshallbeembeddedinthose copper crystals immediatelyadjacent the target and also in crystals located a grain diameter fromthe first group of crystals. The upper transverse side of said reinforcielement is located near the corresponding side of the target butadjacent the 'lower face of the .target. The reinforcing element thusbeing embedded in at least the first two adjacent rows of crystals,extends through the boundary between these rows closest to the sides ofthe target and takes up the stresses which might otherwise be borne bythe crystals.- Because of the high tensile strength of the reinforcingwires, there is no cracking of the copper, even when the target issubjected to higher bombardment than is customary with present typeanodes.

The reinforcing means need not be confined only to the position shown inFigure 1. Besides employing only one reinforcing element locatedadjacent the transverse and longitudinal sizes of the target, we mayalso employ another reinforcing element I! in conjunction therewith, asshown in Figure 8. The other reinforcing element It consists of a mat offine tungsten wire embedded in the copper backing adjacent the lowerfact of the target I I, with some portions thereof being embedded inthat group of copper crystals immediately adjacent the bottom of thetarget I l and the rest, of it being distributed throughout a largeproportion and if desired all of the copper behind the target. As amatter of fact we may employ a mat of tungsten wire which may completelysurround the target that is embedded in the copper.

Even in those tubes which employ targets that cover the entire upperface of the copper, cracking appears in .that portion of the copperadjacent the bottom of said target. To eliminate this objectionablefeature, an annulus I4 is composed of a number of turns of fine tungstenwires which may have their separate turns distorted along their lengths.The annulus is embedded in the copper just below the target and near theouter periphery of the copper backing.

Although our improved X-ray anodes above described may be produced byfollowing any particular series of steps thatis found convenient, wehave employed the following method with good success. A cylindricalsolid graphite element 20 having a portion thereof cut away and beingcomplementary to the configuration of the upper end of the anode to beproduced is placed in a carbon crucible II. The angular face of theelement 2| has a target ll located thereon and held thereto by means ofsmall tungsten wires 22 that are embedded in the carbon form and bentover that face of the target It which is to be coated.

The lower transverse end of the target If rests against the shoulder ofthe carbon form and the longitudinal sides of the target it are locatedinwardly from the sides of the form with the upper transverse end of thetarget located below the upper edge of the form. The reinforcing elementIt is also secured to the block, with the lower transverse side restingupon the shoulder of the form and being contiguous with that end of theface of the target to be coated. the longitudinal and transverse sidesof the reinforcing element l2 extending along and being contiguous withthe corresponding sides of the target ll.

Our invention contemplates the employment of any type of reinforcement.We have found that good results are obtained by forming a reinforc ingelement of basket weave design. This may be produced by employing aforming element 25 having a plurality of rows of spaced posts definingthe length and breadth of the weave to be-pro duced. A wire of tungstenabout 10 mils. in -di- 25 target it and the reinforcing means I! affixedg5 thereto may be treated in a hydrogen-furnace so that their surfacesshall be absolutely oxygen free.

The button H and reinforcement I! may, if

desired, be so treated before mounting on the A9 carbon form. In eithercase the target andrein forcing element are subject to hydrogen 'treat,ment at about 1500 degrees centigrade for about an hour. Added to thecrucible containing the .form 20 to which are amxed the button it andreinforcement I2 is a short rod of copper 24.

The crucible and its contents are placed in "a hydrogen furnace 23 andthe same are heated .in any convenient manner in order to fuse the ofthe target and the coating as separate and distinct operations, we mayaccomplish: both results in a single operation. For these purposes theform 2., the target If and the reinforcing element assembled as shown inFigure 5 may be placed in an open boat with the target face to be coateduppermost. A mass of pure copper shavings is placed on that face to becoated. This group of elements is inserted in a hydro gen furnace wherethey are heated in the pres: ence of a stream of pure hydrogen whichcleans the target by reducing any oxide present there: on. The copperfuses and flows onto the target and reinforcing element and wets thesame.

In this heating step, as in the first fusion step heretofore set forth.the copper is maintained at or above its fusion temperature and in thepresence of pure hydrogen for such a length of time that the tungstenbutton and the tungsten reenforcing element may be completely wetted bythe copper. The presence of hydrogen at the temperatureof copper fusionreduces any copper or tungsten oxides that may have been present. Thus agood bond between the copper and the target II and reenforcing elementis obtained, with the copper extending about one-sixteenth of an inchand preferably of less thickness than that required for the productionof a copper coating having a honeycomb structure due to large hydrogenabsorption. This slug is subjected, to the same subsequent operations asis the slug 26 hereinafter identified.

, The slug 26, as shown in Figure 6 and consisting of the carbon form,the target I I, reinforcing element l2 and the copper 24 is removed fromsaid crucible and placed in a longer crucible II. The crucible 21,together with its contents, is placed in a long furnace. Inserted insaid crucible is also a volume of copper 28 that is large as comparedwith the volume of copper 2|.

Either pure nitrogen or an admixture of 90 percent nitrogen and percenthydrogen is continually passed through this furnace which is heated tofuse the copper. The entire mass of copper is rendered molten and thenallowed to cool. The bar which consists of the carbon form 20, thebutton ll, reinforcing element i2 and a single copper backing iswithdrawn from the furmace and the carbon backing is detached from therod leaving our X-ray anode which is then cleaned and polished.

Although our invention has been described with some particularity it isto be limited only by the prior art because it is susceptible tonumerous modifications, some of which we ourselves have illustrated andbriefly described.

What is claimed:

1. An anode for an X-ray tube comprising a composite unit including aplurality of metallic constituents of diiierent compositions and havingdiiferent coeflicients of linear expansion, "said constituent whosecoefficient of linear expansion is the lower having a high meltingpoint, filamentary means separate from the remaining metallicconstituents and totally imbedded in said constituent whose coeihcientof linear expansion is the higher for reducing the tendency of said lastnamed constituent to cracking upon repeatedly raising and lowering thetemperatures of said constituents, and without affecting the thermalconductivity between said constituents, the fusion point of saidfilamentary means being higher than that of said constituent whosecoefficient of linear expansion is the higher, said filamentary meansbeing disposed immediately adjacent the surface of contact between saidmetallic constituents.

2.1m X-ray anode comprising a composite unit including a plurality ofmetallic constituents, one of said constituents being composed of arefractory metal and another of said constiuents composed of a metalwhose melting point is much lower than that of said refractory metal,the coefficients of linear expansion of said constituents beingdifferent, filamentary means separate from the remaining metallicconstituents and totally imbedded in said metal of lower melting pointfor reducing the tendency of said metal of lower melting point tocracking upon repeatalumnae edly raising and lowering the temperaturesof the same, and without affecting the thermal con- -metallicconstituents.

- 3. An electrode for an electric discharge device comprisinga body ofrefractory metal and.

a body of metal having high heat and electrical conductivitycharacteristics, said bodies being contiguously joined together, andmeans separated from said refractory metal body and totally imbedded insaid second mentioned body forming a layer having an average coefficientof linear expansion intermediate that of the two bodies to take up someof the stresses which would otherwise be borne by said second mentionedbody to reduce the tendency of said second mentioned body to cracking,without affecting the thermal conductivity between said bodies. saidmeans being located adjacent the surface of contact between said bodies.

4. An electrode for an electric discharge device comprising a body ofrefractory metal and a body of metal having high heat and electricalconductivity characteristics contiguously joined together, andfilamentary means separate from said refractory metal body and totallyimbedded in that zone of said second mentioned body which normallycracks upon repeatedly raising and lowering the temperatures of saidbodies to form a layer having an average coeflicient of linear expansionintermediate that of the two bodies, said means reducing the tendency ofsaid second mentioned body to cracking at that zone upon saidtemperatures taking place, without aifecting the thermal conductivitybetween said bodies, said zone being adjacent the surface of contactbetween said bodies.

5. An X-ray anode comprising a target joined to a body of metal of highheat and electrical conductivity characteristics, and means separatefrom said target for taking up some of the stresses that otherwise wouldbe borne by said body and forming a layer having an average coeflicientof linear expansion intermediate said target and body to reduce thetendency of said body to cracking upon repeatedly raising and loweringthe temperatures of said target and body, without affecting the thermalconductivity between said target and body, said means being totallydisposed in said body adjacent the contacting surface between said bodyand target.

6. An X-ray anode comprising a body of refractory metal and a body ofmetal having high heat and electrical conductivity characteristicsjoined together, and means separate from said refractory metal body forreducing the tendency of said second mentioned body to cracking, withoutaffecting the thermal conductivity between said bodies, said means beingtotally imbedded in said second mentioned body to form a layer having anaverage coefficient of linear expansion intermediate that of the twobodies, with por- Joined together, and reinforcing means separate a fromsaid refractory metalbody totally imbedded in that zone of said secondmentioned body which otherwise would crack and forming a layer having anaverage coeiiicient of linear expansion intermediate that of the twobodies to reduce the.

tendency of said cracking it that zone upon raising and lowering thetemperatures of said bodies, and without aflecting the thermalconductivity between said bodies, said zone being located'adjacent thecontacting surface of said bodies.

8. An x-ray anode comprising a target, a body of metal having high heatand electrical conductivity characteristics, said target and body beingcontiguously joined together, and filamentary means separated from saidtarget and totally imbedded in said body to form a layer having acoefficient of linear expansion intermediate that of the twobodies forreducing the tendency of said body to cracking upon repeatedly raisingand lowering the temperatures of said target and body, without aflectingthe thermal conductivity therebetween, said means having portionsthereof imbedded in the crystals of said body immediately adjacent saidtarget and in the crystals of said body adjacent said first mentionedcrystals. 7

9. An article of manufacture comprising a composite unit including aplurality of metallic constituents of different compositions and havingdiil'erentcoeflicients of linear expansion, one of said constituentscomposed of a metal whose melting point is lower than that of saidrefractory metal, and filamentary means imbedded in said metallicconstituent of lower melting point for reducing the tendency of saidlower melting point metal to cracking upon repeatedly raising andlowering the temperature of said constituents, said filamentary meansbeing of zig-zag design along a portion of its length, the melting pointof said filamentary means being higher han that of said metal of lowermelting point.

10. An article of manufacture comprising a composite unit including aplurality of metallic constituents of different compositions and havingiiiferent coeflicients of linear expansion, one of said constituentsbeing composed of a refractory metal and another of said constituentsbeing composed of a metal whose melting point is materially lower thanthat of said refractory metal, a filamentary means simulating a basketweave imbedded in said metal of lower melting point to reduce thetendency of the same to cracking, said means composed of a substancewhose melting point is higher than that of said metal of lower. meltingpoint. 11. An article bf manufacture comprising a refractory metallicbody, another metallic body of lower melting point, said second bodybeing joined to and in contact with said first mentioned body, and areinforcing means imbedded in said second metallic body to form a layerhaving a coeiiicient of linear expansion intermediate that of the twobodies for reducing the tendency of said second metallic body tocracking upon repeatedly raising and lowering the temperatures of saidbodies, the fusion point of said means being greater than that of saidsecond body, said reinforcing means being disposed immediately adjacentthe surface of contact between said bodies without aiiecting the thermalconductivity between said bodies.

izanarticleoi'manui'achirecomprisinga button composed of a refractorymetal body and a bodyhavinghighheat and electrical conductivitycharacteristics, said bodies being joined together, and means separatefrom said metal body imbedded in said second. mentioned body and forminga layer having a coeiiicient of linear expansion intermediate that ofthe two bodies located adjacent the contacting surface of said bodieswithout affecting the thermal conductivity therebetween for reducing thetendency of said second mentioned body to cracking, said means having atensile strength which exceeds that of said second mentioned body.

13. An x-ray anode comprising a target and a body of metal of highthermal and electrical conductivity characteristics joined together, thecoeflicients of linear expansion of said target and body beingdifferent, and means adjacent the surface of said contact between saidtarget and body and separated therefrom and being imbedded in said bodywithout affecting the thermal conductivity between said body and saidtarget for reducing the tendency of said body to cracking uponrepeatedly raising and lowering the temperature of said target and body,said means composed of a whose tensile strength is greater than that ofsaid body, said means having a melting point which is higher than thatof said body.

14. An X-ray anode comprising a target and a body of metal having goodthermal and electrical conductivity characteristics joined together, thecoeiiicients of linear expansion of said target and body beingdifferent, filamentary means adjacent said target and separatedtherefrom and imbedded in that zone'of said body which is subjected tohigh stresses without meeting the thermal conductivity between saidtarget and said body, said means composed of a substance having a highertensile strength than that of said body and also having a higher meltingpoint than that of said body, said means adapted to take up some of thestresses at that zone which mightotherwisebebomebysaidbodyandthustoreducethe tendency of said body tocracking upon repeatedly raising and lowering the temperature of saidtarget and body, said zone being located adjacent the surface of contactbetween said target and body.

15. An X-ray anode comprising a target, a

body of metal having high heat and electrical conductivitycharacteristics, said target and body being contiguously joinedtogether, and filamen tary means separated from said target imbedded insaid body and forming a layer having a coeiiicient of linear expansionintermediate that of said target and said body located adjacent thesurface of contact between said target and body without affecting thethermal conductivity therebetween for reducing the tendency of said bodyto cracking upon repeatedly raising and lowering the temperatures ofsaid target and body, said means composed of a substance having a highermelting point and a higher tensile strength than does said body.

FRANK H. DRIGGS. HARRY W. HIGHRITER.

